Field of the Invention
The present invention relates to an imaging apparatus that images a subject so as to generate electronic image data.
Description of the Related Art
In recent years, photographing that is appropriate to each of the various photographic scenes has been able to be performed by using an imaging apparatus such as a digital camera or a digital video camera. As an example, a technology is known for performing AE (Automatic Exposure) processing for automatically switching exposure according to a diaphragm value even when the diaphragm value is changed in the middle of moving image photographing (Patent Document 1). In this technology, AE processing is smoothly performed by changing an exposure time of an image sensor that generates image data in the middle of a period from the start to the end of the driving of a diaphragm on the basis of information relating to a driving speed of the diaphragm that has been received from an interchangeable lens.
FIG. 15 is a schematic diagram illustrating a situation in which a moving image is photographed by using a conventional imaging apparatus. Under the situation illustrated in FIG. 15, when a photographer performs a panning operation (in a direction of an arrow P) from a dark visual field area to a bright visual field area by using an imaging apparatus, a moving image may be unnaturally displayed due to a problem of exposure adjustment of a camera.
As an example, as illustrated in FIG. 16, luminance may change in the middle of the panning operation, and a flicker may be generated on a screen. Specifically, Wn+1 and Wn+2 in FIG. 16 illustrates screens in a case where prediction is performed in a direction in which a camera closes a diaphragm because a subject becomes bright as a result of the panning operation, but, as an example, when a change in a diaphragm value of an interchangeable lens is mechanically greater than a predicted change, the diaphragm is excessively closed such that underexposure occurs.
In recent years, imaging apparatuses installed with a CMOS (Complementary Metal Oxide Semiconductor) sensor have been popular. In the CMOS sensor, rolling shutter reading is performed, and therefore there is a problem caused by a rolling shutter scheme. In the rolling shutter scheme, an exposure timing on the first read line is different from that on the last read line. Therefore, when a diaphragm changes during exposure, a stored amount of light varies according to a vertical direction of a line, and this results in unevenness of brightness (a rolling shutter effect) in a vertical direction of a screen.
FIG. 17 is a diagram explaining an example in which a screen that has unevenness of luminance in a vertical direction is displayed in the rolling shutter scheme. As illustrated in Wn+1 and Wn+2 in FIG. 17, due to the rolling shutter effect, unevenness of luminance is generated in a vertical direction of a screen in the middle of a panning operation.
In order to solve the problem above, a technology has been proposed for reducing the unevenness above by obtaining a diaphragm value from an interchangeable lens in time series in a cycle synchronizing with a frame rate of an image sensor during photographing of a moving image, and setting exposure conditions such as an exposure time or ISO sensitivity on the basis of a diaphragm value in subsequent exposure that has been predicted using the time-series data (Patent Document 2).
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2010-2900
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2013-31010